1. Field of the Invention
The present invention relates to a method of heating a semiconductor integrated circuit device and, more particularly, to a method of heating a semiconductor substrate capable of preventing defects by implanting.
2. Description of the Related Art
Ion implantation for forming an impurity layer in a predetermined region is generally known as a technique of manufacturing a semiconductor integrated circuit. The ion implantation is a technique of accelerating an ionized element and implanting it into a semiconductor substrate and it is widely used as a method of implanting arsenic (As), antimony (Sb) or the like into a semiconductor substrate.
The ion implantation technique has not only various advantages but also disadvantage. When ions of high energy (10 KeV to several hundreds of KeV) serving as impurity elements are implanted into a semiconductor substrate, they collide with atoms constituting semiconductor crystal. Then, the ions which have the energy much higher than the atomic displacement energy in the crystal cause a number of defects in lattice in the crystal. The semiconductor substrate is thus heated to activate the impurity elements and recrystallize the impurity layer after the ions are implanted into the substrate.
As a well-known method of heating a semiconductor substrate, there is a hot zone method using an electric furnace anneal apparatus. In this apparatus, a jig for housing an ion-implanted semiconductor substrate is inserted into a high-temperature silica tube heated by resistance heating to heat the semiconductor substrate.
The semiconductor substrate inserted into the silica tube is entirely heated by the electric furnace anneal apparatus and its temperature is increased both on the surface on which an impurity layer is formed and on the undersurface opposite to the surface.
Crystal having defects in lattice or amorphous crystal is recrystallized not only in the direction from the interface (between the substrate and impurity layer) having complete crystallization to the surface but also in the direction from the surface to the interface. The defects in lattice are thus caused by grain growth or the like in the impurity layer in a region where the surfaces recrystallized from both the directions meet each other. If an amorphous region into which ions of high dose are implanted is heated, a great number of defects in lattice are generated in the recrystallized surface regions and the internal region of the impurity layer. And the defects in lattice cause severe defects in the crystal of an epitaxial layer grown onto an ion-implantation layer.
The anneal apparatus serves as a heating source for resistance heating. An RTA (Rapid Thermal Anneal) system wherein an infrared lamp serves as a heating source, has been considered and, in this system, a semiconductor substrate into which impurity elements are implanted is heated from the surface. Since, however, the substrate is heated from the surface (surface of ion-implantation layer), recrystallization progresses from the surface to cause defects in crystal near the interface of the ionimplantation layer.
If an active circuit element is formed on a semiconductor substrate having defects in lattice, the characteristic deterioration, such as a current leakage at a PN junction, and reduction in injection efficiency of electrons and holes, is caused.